1. Field of the Invention
This invention relates generally to coated articles such as solar cells and solar control transparencies. In one particular embodiment, the invention relates to an amorphous silicon thin film solar cell having an improved underlayer structure. In another embodiment, the invention relates to a solar control transparency having an improved anti-iridescent undercoating.
2. Technical Considerations
A conventional amorphous silicon thin film solar cell typically includes a glass substrate over which is provided a transparent conductive oxide (TCO) contact layer and an amorphous silicon thin film active layer having a p-n junction. A rear metallic layer acts as a reflector and back contact. The TCO has an irregular surface to increase light scattering. In solar cells, light scattering or “haze” is used to trap light in the active region of the cell. The more light that is trapped in the cell, the higher the efficiency that can be obtained. However, the haze cannot be so great as to adversely impact upon the transparency of light through the TCO. Therefore, light trapping is an important issue when trying to improve the efficiency of solar cells and is particularly important in thin film cell design. However, with thin film devices, this light trapping is more difficult because the layer thicknesses are much thinner than those in previously known monocrystalline devices. As the film thicknesses are reduced, they tend toward coatings having predominantly parallel surfaces. Such parallel surfaces typically do not provide significant light scattering.
Another important feature for thin film solar cells is surface resistivity of the TCO. When the cell is irradiated, electrons generated by the irradiation move through the silicon and into the transparent conductive films. It is important for photoelectric conversion efficiency that the electrons move as rapidly as possible through the conductive film. That is, it is desirable if the surface resistivity of the transparent conductive film is low. It is also desirable if the conductive film is highly transparent to permit the maximum amount of solar radiation to pass to the silicon layer.
Conventional solar control transparencies, e.g., glass panels having a solar control coating, can have undesirable iridescence.
Therefore, it would be desirable to provide a coating configuration for a solar cell that enhances electron flow through the transparent conductive oxide, while also enhancing the light scattering and transparency characteristics of the solar cell. It would also be desirable to provide an anti-iridescent undercoating that could be used for solar cells or solar control transparencies.